1. Field of the Invention
The present invention relates to light emitting structures and, more particularly, to a silicon-based light-emitting structure.
2. Description of the Related Art
The vast majority of microelectronic devices are formed in silicon and, over the last several decades, a substantial effort has been directed to refining the reliability and manufacturability of these devices. As a result, silicon-based microelectronic devices have become dependable and inexpensive commodity items.
To take advantage of the existing silicon-based knowledge and infrastructure, there is a great interest in integrating active optical components into these microelectronic devices. Silicon, however, is an indirect band gap semiconductor material which, unlike a direct band gap semiconductor material, has a low photon emission efficiency. As a result, silicon is considered a poor source of electroluminescent radiation.
Although the photon-generation mechanism is not well understood, one source of visible light from silicon is a reverse biased p-n junction under avalanche breakdown conditions. Avalanche breakdown occurs when the p-n junction is reverse biased to the point of where the electric field across the junction accelerates electrons into having ionizing collisions with the lattice.
The ionizing collisions generate additional electrons which, along with the original electrons, are accelerated into having additional ionizing collisions. As this process continues, the number of electrons increases dramatically in a very short period of time, producing a current multiplication effect.
Building on this principle, Snyman, et al. in A Dependency of Quantum Efficiency of Silicon CMOS n+pp+LEDs on Current Density, IEEE Photonics Technology Letters, Vol. 17, No. 10, October 2005, pp 2041-2043, have reported that the efficiency of light emission from silicon can be substantially increased by utilizing a reverse biased p-n junction with a wedge-shaped tip that confines the vertical and lateral electric field.
FIGS. 1A-1B show views of a p-n junction structure 100 that illustrate an example of the Snyman, et al. device. FIG. 1A shows a plan view, and FIG. 1B shows a cross-sectional view of structure 100 taken along lines 1B-1B. As shown in FIGS. 1A-1B, structure 100 includes a p-type semiconductor substrate 110, and an n-type well 112 that is formed in substrate 110.
In addition, structure 100 includes a p-type junction region 114 that is formed in n-type well 112, and an n-type junction region 116 that is formed in substrate 110 to contact p-type junction region 114 and form a lateral p-n junction 120. N-type junction region 116, in turn, has a tip-shape.
As further shown in FIG. 1A, structure 100 includes a pair of p-type contact regions 122 that are formed in p-type junction region 114 on opposite sides of the tip of n-type junction region 116. P-type contact regions 122 have higher dopant concentrations than p-type junction region 114. In addition, structure 100 includes a layer of silicon dioxide 124 that is formed on the top surfaces of n-type well 112, p-type junction region 114, and n-type junction region 116.
In operation, a first voltage is placed on p-type junction region 114 via p-type contact regions 122, and a second voltage is placed on n-type junction region 116. The second voltage, which is greater than the first voltage, sets up an electric field across p-n junction 120 that reverse biases junction 120.
As additionally shown in FIG. 1A, the electric field and the relative intensity of the electric field can be illustrated by a group of electric field lines 126. As shown by the electric field lines 126, the relative intensity of the electric field is significantly greater at the tip of n-type junction region 116 than it is at any of the other locations along the periphery of n-type junction region 116.
When photon emission is desired, the second voltage is increased to the point of initiating avalanche breakdown. Since the electric field is significantly greater at the tip of n-type junction region 116, the density of the avalanche current at the tip of n-type junction region 116 is also significantly greater than it is at any of the other locations along the periphery of n-type junction region 116.
As reported by Snyman, et al., structure 100 produces a significant increase in the luminescence intensity, which reached values of up to 1 nW per μM2. The significant increase in current density at the tip of n-type junction region 116 appears to have led to the increase in luminescence intensity.